Air-swept machines for husking or polishing cereal grains are very well known in the art and many different types of said machines are available in the market.
For many years, however, the husking and the polishing operations were carried out in grain mills through the use of different stages, each requiring the use of different machines, due to the fact that the husking of grain was believed to require different rubbing elements as compared to the polishing of cereal grains. This obviously required the provision of intermediate stages for the removal of the husk produced by the husking machines, before the husked grain could be fed to the polishing machines.
In more recent times, a new family of air-swept machines designed to serve both as grain husking and as grain polishing machines was introduced. This type of machines, however, started to be designed as machines having an air-swept treatment chamber formed by a cylindrical abrasive rotor and a polygonal indented screen surrounding said rotor, because it was believed that the use of such polygonal indented screens would increase the efficiency of the apparatus, due to the obstructions produced by the corners thereof on the moving grains, which allegedly would force the grains to be rubbed against each other in said corner areas, accomplishing a more energetic action thereon. The experience gained through the use of said machines throughout the years, however, has proven that said corner areas, rather than effecting the alleged more energetic action on the grains, were areas of heavy accumulation of grains, wherein the grains therefore were not rubbed at all and remained in their original condition throughout the period of treatment.
In order to overcome the above described drawbacks shown by these prior art machines, a new generation of air-swept grain husking and polishing machines was created which, by the use of specially designed screen members, were capable of avoiding the formation of accumulations of untreated grains within the treatment chamber.
One of this new type of machines was described and claimed in U.S. Pat. No. 3,960,068 to Felipe Salete, the same applicant hereof, who describes an air-swept rice polishing machine comprising a treatment chamber for grain which was constituted by a hollow rotor and a cylindrical indented screen surrounding the same. The rotor is preceded by a screw conveyor for forcedly conveying the grain stream upwardly towards said rotor and said rotor has a pair of rectractible knives to retain the movement of the grain at will, whereby the pressure applied by said screw conveyor pushes the grain to be trapped by said rotor, which spins the mass of grains against the action of the indented screen, thus rubbing the grains effectively without accumulation thereof. This machine, however, due to its rotor design, is not capable of husking the grain, whereby an additional husking stage must be incorporated.
One other husking and polishing machine for grains is described and claimed in U.S. Pat. No. 4,292,890 to Salete, which solves the above described problems of the prior art machines, by incorporating a new design of screen and rotor assembly which comprises a cylindrical rotor having two specially designed fluted knives tangentially arranged thereto, such that the grains are gradually pressed when trapped by each knife which is inclined outwardly of the periphery of the rotor, contrary to the direction of movement of the same, and a screen supported by a specially designed screen holder, which comprises two semi-cylindrical screen members attached and fastened to said screen holder by means of a pair of stationary fluted knives having their flutes directed in such a manner that the flow of grains in the treatment chamber is forced downwardly while the stream of grains is pushed upwardly by a screw conveyor provided with an abrasive layer on the forward face thereof, thus producing a high compression of the grains, that are therefore strongly abraded and rubbed both by the screw conveyor abrasive layer and by the screen and rotor assembly, and may therefore be husked and polished in one single machine, although not in one single step, because if husking is desired, the elements of the machine must be adjusted to exercise a stronger action on the grains, whereas if polishing is the preferred function, then the machine must be readjusted to exercise a more gentle action against the grains.
One other grain husking and polishing machine which marks a further advance in the art is that described and claimed in U.S. Pat. No. 4,583,455 also to Salete, that may be regarded as being a remarkable improvement over the machines of the prior art. The general structure of the machine of this U.S. patent is very similar to that of the machine of U.S. Pat. No. 4,292,890, but provides a different type of treatment chamber formed within a specially designed screen and rotor assembly that permits a more efficient rubbing of the grain with a decreased degree of breakage of the same. The screen and rotor assembly of the machine of U.S. Pat. No. 4,583,455 comprises a screen formed by alternate sections of screen material and of abrasive material assembled within a screen holder member which comprises a plurality of vertical channels within which said abrasive sections, which take the form of abrasive blocks, are adjustably mounted. Between each pair of said vertical channels, a corresponding screen section is mounted such that the edges thereof are trapped by said abrasive blocks against the walls of said channels, thus providing alternate abrasive sections for energetically rubbing the grains, spaced between respective alternate sections of screen material to permit the expeditious exit of flour, powder, bran and other impurities of the grain, which are swept by the air circulating through the device; and a rotor which comprises a hollow cylindrical body which is rotatably mounted concentrically within said screen assembly for rotating in unison with a vertical screw conveyor mounted below the above mentioned hollow cylindrical body. The cylindrical body of the rotor is provided with a plurality of radial bores to permit the free passage of air therethrough for sweeping the treatment chamber and also has a plurality of axially extending superficial grooves within each one of which a corresponding abrasive block is mounted to co-act with the abrasive blocks of said screen assembly, said abrasive blocks of the rotor being capable of replacement and of adjustment within the grooves in order to enable the user to adjust the machine for exerting a higher or a lower energetic action to husk and polish the grain passing vertically upwardly of the chamber. By these means, the machine of U.S. Pat. No. 4,583,455 is perfectly capable of performing a husking and a polishing action of the grains in one single step, because the grain stream will be alternately subjected to a strong abrasive and rubbing action between pairs of abrasive blocks, and to a mild rubbing action between a screen section and an abrasive block or a smooth surface of the rotor.
Regardless of the fact that the machines of Salete as described above have represented a considerable advance in the art of grain husking and polishing and have been regarded by the most important grain millers throughout the world as the best machines for this purpose existing in the worldwide marketplace, because any one of said machines accomplish the goals of minimizing grain breakage and the treatment temperature of the grains, thus avoiding agglomeration thereof, considerably decreasing the power consumption per unit of weight of grain treated, providing higher accuracy in the control of the husking and/or polishing operations, etc., which has brought about a considerable improvement in the costs of operation of the mills, as well as an improvement in the quality and uniformity of the treated grain, it is nevertheless to be reminded that very diversified types of grain exist in the producing localities of the world, even for the same species of grain (rice, wheat, corn, etc.) and for the same locality, and that the above described prior art machines are not capable of treating different types and qualities of grain without having to suffer heavy adjustments that therefore require full stoppage of the plant to adjust the machine when a batch of a different grain quality or species is to be treated within the same mill.
Therefore, while very efficient machines are already existing in the market for husking and polishing cereal grains, there remains the need of a machine that may be sufficiently versatile to cope up with the needs of the highly varied types of grains, without however loosing its efficiency for carrying out the husking and/or polishing operations to produce a high quality grain.